Our bodies accumulate toxins and chemicals throughout our lifetime. From what we eat, to what we breath, environmental toxins like lead, mercury and PCBs that do not easily break down can be stored in our own fatty tissues. While it is unsure whether the co-exposure of these chemicals is more harmful that to each one separately, a new study shows that several risk factors are associated with a higher chance of median blood levels for these contaminants.

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In an analysis of data on over three thousand women, Brown University researchers concluded that all but 17.3 percent of the women aged 16 to 49 were at or above the median blood level for one or more of these chemicals, which can then passed to fetuses and babies.

Mercury, lead, and PCBs are of particular interest because they are persistent in the environment and can harm fetal and infant brain development, said study lead author Dr. Marcella Thompson.

"Our research documents the prevalence of women who are exposed to all three of these chemicals," said Thompson. "It points out clearly the need to look at health outcomes for multiple environmental chemical co-exposures."

The study looked at data collected between 1999 and 2004 from women of all different demographics who participated in the Centers for Disease Control and Prevention National Health and Nutrition Examination Survey.

The study found that as women grew older, their risk of exceeding the median blood level in two or more of these pollutants grew exponentially. Researchers explain this risk not only because these chemicals accumulate in the body over time, but also because these women were born before most environmental protection laws were enacted.

The study also found that women who ate fish more than once a week during the prior 30 days had 4.5 times the risk of exceeding the median in two or more of these pollutants and women who drank heavily had a milder but still substantially elevated risk.

However, not all risks increased. Women who had breastfed at least one child for a month had about half the risk of exceeding the median blood level for two or more pollutants. Researchers explained that women pass the pollutants that have accumulated in their bodies to their nursing infants.

Although the study did not measure ill health effects, Thompson said, the data still suggest that women should learn about their risks of co-exposure to these chemicals well before they become pregnant.